The present invention is directed to a process for upgrading light paraffins such as propane, and butanes. Interest in upgrading these light paraffins has been growing due to recent and anticipated changes in refinery processing schemes which resulted and will result in a greater supply of such light paraffins. These changes include: the higher severity operation of the reforming process in order to maintain a high octane rating in the absence of or reduction of the lead content in gasoline; the lowering of reid vapor pressure (RVP) specifications; the increased use of oxygenates such as methyl tertiary butyl ether (MTBE) and ethanol resulting in the removal of butanes from the gasoline pool; the increased demand for jet fuel necessitating increased gas oil hydrocracking resulting in more light gas production, and the increase in operating temperatures in fluidized catalytic crackers resulting in more light gas production. Thus, there is great incentive to investigate means for converting these materials into more valuable liquids such as transportation fuels or chemical feedstocks.
The upgrading or conversion of light paraffinic gases and synthesis gas has previously been carried out in the presence of gallium-based or gallium-containing catalysts wherein such catalysts also contain various types of molecular sieves.
U.S. Pat. No. 4,543,347 (Heyward et al.) discloses a catalyst composition suitable for converting synthesis gas to hydrocarbons which is a mixture of zinc oxide and an oxide of at least one metal selected from gallium and iridium, an oxide of at least one additional metal collected from the elements of Groups IB, II through V, VIB and VIII including the lanthanides and actinides and a porous crystalline tectometallic silicate.
U.S. Pat. No. 4,490,569 (Chu et al.) discloses a process for converting propane to aromatics over a zinc-gallium zeolite. This zeolite optionally may also contain palladium. More specifically, the catalyst composition used in the instant patent consists essentially of an aluminosilicate having gallium and zinc deposited thereon or an aluminosilicate in which cations have been exchanged with gallium and zinc ions wherein the aluminosilicate is selected from the group known as ZSM-5 type zeolites.
U.S. Pat. No. 4,585,641 (Barri et al.) discloses crystalline gallosilicates which may be impregnated, ion-exchanged, admixed, supported or bound for catalyzing a reaction such as alkylation, dealkylation, dehydrocyclodimerization, transalkylation, isomerization, dehydrogenation, hydrogenation, cracking, hydrocracking, cyclization, polymerization, conversion of carbon monoxide and hydrogen mixtures through hydrocarbons and dehydration reaction. The metal compounds which may be used for ion exchange or impregnation may be compounds of any one of the groups of metals belonging to Groups IB, IIB, IIIA, IVA, VA, VIB, VIIB and VIII according to the Periodic Table. Specifically, preferred compounds include copper, silver, zinc, aluminum, gallium, indium, vanadium, lead, antimony, bismuth, chromium, molybdenum, tungsten, manganese, iron, cobalt, nickel, ruthenium, rhodium, palladium, iridium, platinum, radium, thorium and the rare earth metals. Patentees describe their gallosilicate as "Gallo Theta-1" in contradistinction to an MFI-type gallosilicate which has a substantially different X-ray diffraction pattern.
U.S. Pat. No. 4,350,835 (Chester et al.) relates to a catalytic process for converting gaseous feedstocks containing ethane to liquid aromatics by contacting the feed in the absence of air or oxygen under conversion conditions with a crystalline zeolite catalyst having incorporated therein a minor amount of gallium thereby converting the ethane to aromatics. The gallium is present in the catalyst as gallium oxide or as gallium ions if cations in the aluminosilicate have been exchanged with gallium ions. The patent further discloses that the original alkali metal of the zeolite, when it has been synthesized in the alkali metal form, may be converted to the hydrogen form or be replaced by ion exchange with other suitable metal cations of Groups I through VIII of the Periodic Table, including nickel, copper, zinc, palladium, calcium or rare earth metals.
European Patent Specification 0 050 021 discloses a process for producing aromatic hydrocarbons from a hydrocarbon feedstock containing at least 70 wt. % C.sub.2 with a catalyst composition comprising an aluminosilicate having gallium deposited thereon and/or an aluminosilicate in which cations have been exchanged with gallium ions, where the aluminosilicate has a silica to alumina molar ratio of at least 5:1.
European Patent Application 0 107 876 discloses a process for producing an aromatic hydrocarbon mixture from a feedstock containing more than 50 wt. % C.sub.2 through C.sub.4 paraffins. Specifically, the process is carried out in the presence of crystalline gallium-silicate having a SiO.sub.2 /Ga.sub.2 O.sub.3 molar ratio of 25 to 250 and a Y.sub.2 O.sub.3 /GaO.sub.3 molar ratio lower than 1 where Y can be aluminum, iron, cobalt or chromium. The disclosure also teaches a two-step silicate treatment comprising a coke deposition and a coke burn-off with an oxygen-containing gas.
European Patent Application 0 107 875 similarly discloses a process for producing an aromatic hydrocarbon mixture from a feedstock comprising more than 50 wt. % of C.sub.2 through C.sub.4 paraffins. This process is carried out in the presence of a crystalline gallium-silicate, having a SiO.sub.2 /Ga.sub.2 O.sub.3 molar ratio of 25 to 100 and a Y.sub.2 O.sub.2 /Ga.sub.2 O.sub.3 molar ratio lower than 1 where Y can be aluminum, iron, cobalt or chromium.
Other patents that disclose processes for upgrading light paraffins using gallium-containing catalysts include:
U.S. Pat. No. 4,613,716 (McNiff) PA0 U.S. Pat. No. 4,766,264 (Bennett et al.) PA0 U.S. Pat. No. 4,276,437 (Chu) PA0 U.S. Pat. No. 4,629,818 (Burress)
Light paraffinic gases have also been upgraded to liquid aromatics in the presence of crystalline aluminosilicate zeolite catalysts having incorporated therein a minor amount of a metal selected from Groups VIII, IIB, and IB of the Periodic Table. For instance, U.S. Pat. No. 4,210,910 (Chu) discloses copper-zinc-HZSM-5, platinum-HZSM-5, copper-HZSM-5, and zinc-HZSM-5 catalysts suitable for upgrading a gaseous paraffinic hydrocarbon feed to aromatic compounds.
U.S. Pat. No. 4,704,494 (Inui) discloses a process for the conversion of low molecular paraffin hydrocarbons to aromatic hydrocarbons in the presence of metallosilicates wherein the metal is Al, Ga, Ti, Zr, Ge, La, Mn, Cr, Sc, V, Fe, W, Mo, or Ni.
International Application No. PCT/GB84/00109 (International Publication Number: WO84/03879) (Barlow) discloses an aromatization process utilizing a catalyst having a Group VIII metal in combination with a galloaluminosilicate.
It has now been discovered that C.sub.3 through C.sub.5 light paraffins can most effectively be upgraded by the catalytic process of the present invention minimizing methane and ethane production while simultaneously maximizing the production of benzene, toluene, and xylenes.
The process of the present invention involves the use of an AMS-1B crystalline borosilicate molecular sieve. This sieve is disclosed in U.S. Pat. Nos. 4,268,420 and 4,269,813 (both to Klotz) both of which are incorporated herein by reference. The '420 patent broadly discloses the use of the AMS-1B crystalline borosilicates for various hydrocarbon conversion processes and chemical adsorption. Some of the hydrocarbon conversion processes for which the borosilicates appear to have relatively useful catalytic properties are fluidized catalytic cracking; hydrocracking; the isomerization of normal paraffins and naphthenes; the reforming of naphthas and gasoline-boiling-range feedstocks; the isomerization of aromatics, especially the isomerization of alkylaromatics, such as xylenes; the disproportionation of aromatics, such as toluene, to form mixtures of other more valuable products including benzene, xylene, and other higher methyl-substituted benzenes; hydrotreating; alkylation; hydrodealkylation; hydrodesulfurization; and hydrodenitrogenation. They are particularly suitable for the isomerization of alkylaromatics, such as xylenes, and for the conversion of ethylbenzene. The AMS-1B borosilicates, in certain ion-exchanged forms, can be used to convert alcohols, such as methanol, to useful products, such as aromatics or olefins.
It should also be noted that hydrogen processing catalysts containing an AMS-1B borosilicate molecular sieve coupled with catalytic metal components are also known. For instance, U.S. Pat. No. 4,434,047 (Hensley, Jr. et al.) discloses a catalytic dewaxing hydrotreating process using a catalyst containing a shape-selective cracking component such as an AMS-1B borosilicate molecular sieve, and a hydrogenating component containing Cr, at least one other Group VIB metal and at least one Group VIII metal. U.S. Pat. No. 4,268,420 similarly discloses an AMS-1B crystalline borosilicate which can be used in intimate combination with a hydrogenating component, such as tungsten, vanadium, molybdenum, rhenium, nickel, cobalt, chromium, manganese, or a noble metal, such as platinum or palladium, or rare earth metals, where a hydrogenation-dehydrogenation function is to be performed.
U.S. Pat. No. 4,563,266 (Hopkins et al.) discloses an AMS-1B crystalline borosilicate molecular sieve combined with at least one Group VIII noble metal for use in a catalytic dewaxing process. U.S. Pat. No. 4,738,768 (Tait et al.) likewise discloses the use of an AMS-1B borosilicate in a hydrocarbon pour point reducing process.
U.S. Pat. No. 4,451,685 (Nevitt et al.) discloses a process to convert propylene to gasoline blending stock products. Specifically, C.sub.2 through C.sub.3 olefins are converted to a mixture of C.sub.4 through C.sub.8 aliphatics and C.sub.6 through C.sub.9 aromatics in the presence of hydrogen and a catalyst. The catalyst employed is a crystalline AMS-1B borosilicate that may be impregnated with catalytically active materials including the metals of Groups IB, IIA, IIIA, IIIB, IVB, VB, VIB, VIIB and VIII and rare earth elements.
U.S. Pat. No. 4,433,190 (Sikkenga et al.) discloses a process to convert substantially linear alkanes such as normal alkanes having two to twenty carbon atoms to dehydrogenated and isomerized products in the presence of hydrogen and an AMS-1B crystalline borosilicate-based catalyst composition. This catalyst contains a noble metal and may also contain an ion or molecule of a Group IB, IIIB, IVB, VB, VIB, VIIB or VIII metal or a rare earth element.
Finally, U.S. Pat. No. 4,766,265 (Desmond) teaches a process for the conversion of ethane to liquid aromatic compounds using a catalyst containing a gallium impregnated molecular sieve with both a rhenium component and a metal selected from the group consisting of nickel, palladium, platinum, rhodium and iridium. The molecular sieve can be an alumino-, gallo-, or borosilicate. The '265 process is directed to handling ethane rich feedstocks ranging from 100% ethane to a feedstock containing only minor amounts of ethane in a feedstock predominantly of hydrogen, methane and relatively minor amounts of C.sub.2 -C.sub.5 olefins and C.sub.3 -C.sub.5 paraffins.
In contrast to the '265 process, the process of the present invention is directed to the conversion of a hydrocarbon gas rich in C.sub.3 through C.sub.5 light paraffins, preferably a feedstock rich in either C.sub.3 and/or C.sub.4. Further, the process of the present invention does not require the presence of a rhenium metal component in the catalyst.
It has now been discovered that C.sub.3 through C.sub.5 paraffins can most effectively be upgraded by the catalytic process of the present invention minimizing methane and ethane production while simultaneously maximizing the production of benzene, toluene and xylenes.